The invention relates to an intraoral distractor for callus distraction in the human lower jaw with a proximal (posterior) and a distal (anterior) fixation part and a first displacement mechanism for a linear lengthening of the distance between the two fixation parts so as to lengthen the body of the mandible or the ramus of the mandible in the area of an osteotomy.
Such an intraoral distractor is known from the German Patent Application DE-A1-195 37 023.
A distractor for the callus distraction in the human lower jaw is a combined surgical-orthodontical apparatus which allows the lengthening of a callus in order to correct occlusal problems, malformations, asymmetries of the mandible and miss-relations between upper and lower jaw which can be congenital or acquired, the latter for example through an accident.
Such distractors allow the linear lengthening of the mandibular ramus (ramus mandibulae) or the horizontal part of the mandible (corpus mandibulae) in the area of an osteotomy, i.e. where the bone has been cut. Furthermore, it is possible to change the angle of the mandibular angle in order to turn the occlusal plane of the lower dentition to adjust it to the occlusal plane of the upper dentition. In order to achieve this, the ramus and the corpus of the mandible are turned in the area of the osteotomy around an angle in their relation.
It is important to distinguish between intraoral and extraoral distractors for callus distraction in the human mandible. Both distractors have fixation parts which are fixated to the mandible on both sides of the required osteotomy. In the case of an extraoral distractor, fixation pins extend from these fixation elements in a percutaneous manner to the extraoral displacement units, e.g. threaded bolts or shafts and tubes. The advantage of such extraoral distractors is the good accessibility to the displacement units from outside. However, they have the disadvantage that the fixation pins are lead through the skin which results in scars depending on the size of the wound.
Intraoral distractors are placed within the oral cavity including the displacement units. Therefore, such distractors do not require the percutaneous placement of pins or fixation units. However, the space available within the oral cavity is limited which makes it difficult to optimally place the corresponding displacement units such that they are easily accessible.
The distractor, as it is known from German Patent Application DE-A1-195 37 023, comprises small fixation parts which are displaceable relative to each other. One fixation part relates to a tube, while the other relates to a threaded bolt which is guided by the tube. The threaded bolt can be turned within the tube such that, by turning, the distance between the two fixation parts can be continuously and linearly changed.
Furthermore, when installing distractors on the mandible, care must be taken not to harm the alveolar nerve (nervus alveolaris inferior) which runs within the canalis mandibulae and exits the corpus mandibulae at the foramen mentale. This nerve grants the sensibility of the lower lip and must not be harmed by fixation parts which are screwed into the mandible.
A further appliance for the fixation of bone segments, which can also be used in the area of the mandible, is known from the German Patent Application DE-A1-195 03 609. This device comprises a multi-part fixation which has single fixation units, each related to a sequence of toothed racks. The single fixation units are each anchored to the mandible by percutaneous pins. Between the two fixation units an osteotomy can be positioned. The change in position of the corresponding two bone segments is achieved by a fixation unit which is linearly moved along the toothed rack. Such a mechanism is only applicable in an extraoral form.
A further distractor is known from the U.S. Pat. No. 5,203,783. This device comprises a traction part with a housing out of which a cylindrical part similar to a piston can be moved out. At the end of the cylindrical portion, there is a disc which is fixated to the housing with a pin on the one side while it has a unit for fixation to the bone on the opposite side. By displacing--i.e., lengthening or shortening--of the piston-like cylindrical portion the disc is turned such that, with this turning, there is also an angular turn of the fixation part fixed to the bone. This device is quite large and therefore not usable as a distractor for callus distraction in the mandible, especially not in an intraoral form of a distractor.